fix(@angular-devkit/build-angular): downlevel class private methods when targeting Safari <=v15

This commits enables `@babel/plugin-proposal-private-methods` when targeting Safari <=v15 as this is needed to handle private class methods when using `@babel/plugin-proposal-class-properties`.

Closes #24411

Author: alan-agius4

packages/angular_devkit/build_angular/src/babel/presets/application.ts

@@ -197,7 +197,10 @@ export default function (api: unknown, options: ApplicationPresetOptions) {
     // downlevel class properties by ensuring the class properties Babel plugin
     // is always included- regardless of the preset-env targets.
     if (options.supportedBrowsers.some((b) => safariClassFieldScopeBugBrowsers.has(b))) {
-      includePlugins.push('@babel/plugin-proposal-class-properties');
+      includePlugins.push(
+        '@babel/plugin-proposal-class-properties',
+        '@babel/plugin-proposal-private-methods',
+      );
     }
 
     presets.push([

tests/legacy-cli/e2e/tests/misc/safari-15-class-properties.ts

@@ -1,56 +1,70 @@
-import { expectFileToExist, readFile, writeFile } from '../../utils/fs';
+import assert from 'node:assert';
+import { expectFileToExist, readFile, writeFile, replaceInFile } from '../../utils/fs';
 import { ng } from '../../utils/process';
-import { updateJsonFile } from '../../utils/project';
 
 const unexpectedStaticFieldErrorMessage =
   'Found unexpected static field. This indicates that the Safari <=v15 ' +
   'workaround for a scope variable tracking is not working. ' +
   'See: https://github.com/angular/angular-cli/pull/24357';
 
 export default async function () {
-  await updateJsonFile('angular.json', (workspace) => {
-    const build = workspace.projects['test-project'].architect.build;
-    build.defaultConfiguration = undefined;
-    build.options = {
-      ...build.options,
-      optimization: false,
-      outputHashing: 'none',
-    };
-  });
+  // Add a private method
+  await replaceInFile(
+    'src/app/app.component.ts',
+    `title = 'test-project';`,
+    `
+      #myPrivateMethod() { return 1 }
+
+      constructor() {
+        console.log(this.#myPrivateMethod)
+      }
+
+      title = 'test-project';`,
+  );
 
   // Matches two types of static fields that indicate that the Safari bug
   // may still occur. With the workaround this should not appear in bundles.
   //   - static { this.ecmp = bla }
   //   - static #_ = this.ecmp = bla
   const staticIndicatorRegex = /static\s+(\{|#[_\d]+\s+=)/;
 
-  await ng('build');
+  await ng('build', '--configuration=development');
   await expectFileToExist('dist/test-project/main.js');
   const mainContent = await readFile('dist/test-project/main.js');
-
   // TODO: This default cause can be removed in the future when Safari v15
   // is longer included in the default browserlist configuration of CLI apps.
-  if (staticIndicatorRegex.test(mainContent)) {
-    throw new Error(unexpectedStaticFieldErrorMessage);
-  }
+  assert.doesNotMatch(mainContent, staticIndicatorRegex, unexpectedStaticFieldErrorMessage);
 
   await writeFile('.browserslistrc', 'last 1 chrome version');
-
-  await ng('build');
+  await ng('build', '--configuration=development');
   await expectFileToExist('dist/test-project/main.js');
   const mainContentChromeLatest = await readFile('dist/test-project/main.js');
 
-  if (!staticIndicatorRegex.test(mainContentChromeLatest)) {
-    throw new Error('Expected static fields to be used when Safari <=v15 is not targeted.');
-  }
+  assert.match(
+    mainContentChromeLatest,
+    staticIndicatorRegex,
+    'Expected static fields to be used when Safari <=v15 is not targeted.',
+  );
+  assert.match(
+    mainContentChromeLatest,
+    /#myPrivateMethod/,
+    'Expected private method to be used when Safari <=v15 is not targeted.',
+  );
 
   await writeFile('.browserslistrc', 'Safari <=15');
 
-  await ng('build');
+  await ng('build', '--configuration=development');
   await expectFileToExist('dist/test-project/main.js');
   const mainContentSafari15Explicit = await readFile('dist/test-project/main.js');
+  assert.doesNotMatch(
+    mainContentSafari15Explicit,
+    staticIndicatorRegex,
+    unexpectedStaticFieldErrorMessage,
+  );
 
-  if (staticIndicatorRegex.test(mainContentSafari15Explicit)) {
-    throw new Error(unexpectedStaticFieldErrorMessage);
-  }
+  assert.match(
+    mainContentSafari15Explicit,
+    /var _myPrivateMethod/,
+    'Expected private method to be downlevelled when Safari <=v15 is targeted',
+  );
 }